In a primary configuration, a skateboard comprises an elongated, suitably designed footboard from which two pairs of rollers are suspended. Optionally, a skateboard can further comprise supplementary equipment, e.g. a brake, a flywheel, a lamp, a marker, a buffer, etc. Normally, in the course of skateboarding, turning is made possible when the footboard of skateboard is parallel to the skateboarding path while riding straight by slanting the footboard to either side with respect to its longitudinal axis. This action can be realized by means of a specific suspension of the rollers. For performing a curve, the inclination of the footboard results in a front and a rear roller, the "inner" rollers with respect to the curve, being mutually drawn together, whereas the other two rollers, the "outer" ones with respect to the curve, are mutually drawn apart.
It is obvious that proper propelling of the skateboard is performed by the rider pushing off from the ground (and/or by riding downhill) so that a skateboard/rider-system as a physical phenomenon, i.e. skateboard and rider functionally united into a combined, independent unit, can be discussed merely within the period of the consumption of mass forces previously accumulated (or--in the case of riding downhill, by using gravity force).
Attempts to assign to a skateboard/rider-system the character of a physical phenomenon without using gravity force or a special source of energy, respectively, i.e. solely on the basis of the physical engagement of the rider, are known.
From U.S. Pat. No. 4,915,403 to Wild et al. a "skateboard with a mechanical drive" is known, having a footboard which is, in the area of the middle of the longitudinal extension of the footboard, transversely divided into a front, fixed section, and a rear, pedal section. The footboard sections are interconnected by a skateboard frame. The pedal section is, by means of linkages comprising push rod, a crankshaft and a toothed segment, as well as by means of a gear train bound to the toothed segment and comprising four pairs of toothed wheels and a termination toothed wheel, which is bound to a roller shaft of the rear skateboard rollers, motion-transferably interconnected with respective skateboard rollers, each of which is connected to the shaft by means of an overrunning clutch.
According to the above reference, the skateboard provided essentially has the same height as skateboards without propelling gearings, and diverse operational possibilities are retained, such as ease in negotiating curves and maneuverability.
However, the height of the skateboard of Wild can only be discussed in connection with the front, i.e. fixed, footboard section of the skateboard, not in connection with the rear, i.e. pedal section, except at a position when its pedal function is arrested which, however, is not in confirmity with the primary aim or object of the solution. Analogously, regarding the "diverse possibilities" the following points are noted. Curves can easily be negotiated and the skateboard easily handled under the condition only that the pedal function is arrested, i.e. both footboard sections straightened to be coplanar. In the state when the skateboard is physically pushed, only the rider's foot resting on the front footboard section of the skateboard is left to accomplish normal riding ("normal" meaning the possibilities offered by the skateboards without propelling gears). Thus, the maneuverability is obviously and considerably affected. So, for example, the possibility of making jumps, when the pedal section is lifted, is totally excluded.
Further, the length of the footboard of the skateboard is limited to a length of at least two feet and there is a danger of toppling on one side or the other with respect to the direction of riding as well as backwards over the rear rollers (as a consequence that propelling tends to jerk the skateboard from under the rider's feet).
From the functional point of view the known solution shows a further disadvantage which cannot be neglected, namely the driving torsional moment is enforced intermittently: a driving phase is followed by an idle one, the latter is followed by a driving phase, etc.